Simple behaviors are generated within the central nervous system by limited neuronal networks call Central Pattern Generators (CPGS). In isolation, these networks produce stereotyped motor patterns, but in vivo, they interact with extensive modulatory and sensory inputs to produce the normal variety of related behaviors. A dysfunction of these modulatory inputs to produce the normal variety of related behaviors. A dysfunction of these modulatory inputs would seriously limit the spectrum of behavior generated by the CPG. The mechanisms involved in modulation of neuronal circuits are not well understood. Our hypothesis is that modulatory inputs alter the physiological organization of the network from moment to moment, producing a variety of different motor patterns from one network of cells. To test this hypothesis, we will study the actions of three amines, dopamine, octopamine and serotonin, as modulators of the CPG for the pyloric rhythm in the lobster stomatogastric ganglion. These amines can produce distinctive variants on the pyloric motor pattern when applied to the isolated stomatogastric ganglion. We will combine electrophysiological and pharmacological techniques to pursue the following goals: 1) Study the biophysical actions of amines on ion currents in different cells in the pyloric CPG, to determine the extent of diversity and convergence in modulator actions on different cells in a single circuit. 2) Study the second messenger mechanisms used by amines in different cells, to determine whether a modulator acts by single or multiple mechanisms within a neuronal circuit. 3) Analyze amine modulation of synaptic transmission in the circuit, to show that modulators can change the "wiring diagram" of the circuit from moment to moment. 4) Study the anatomy and physiological activity of cells that deliver the amines to the stomatogastric ganglion, to determine the behavioral context for amine modulation of the pyloric motor pattern. This work will further our understanding of how a single anatomically defined neuronal network can be modulated to produce a series of related functional circuits, each generating a unique variant on the basic motor pattern.